Of the various types of electrochemical energy storage systems, the lithium ion cell is currently the most commonly used for powering vehicles as well as portable electronic devices. For example, battery electric vehicles can use one or more battery packs containing cells having a cylindrical or other shape. In general, a lithium ion cell includes a cathode material and an anode material with a separator between them, and an electrolyte that facilitates the electrochemical processes involved in charging and discharging the cell.
In some lithium ion cells, the cathode material is made using a lithium nickel cobalt aluminum oxide. For example, this material can be manufactured by mixing a lithium salt with a precursor material, and baking the mixture so that it becomes a powder. This material will ultimately be formed into the desired shape of the cathode, such as a sheet. The formed lithium nickel cobalt aluminum oxide is relatively sensitive after the baking. For example, residual lithium can be present in form of lithium carbonate or lithium hydroxide. Significant residual lithium remaining in the cathode material after the cell is assembled can be detrimental to cell life. For this purpose, a washing step has been introduced into the manufacturing process. The washing can stabilize the lithium nickel cobalt aluminum oxide by forming a nickel oxyhydroxide surface on the particles.
After the washing, the material should be dried to reduce its moisture level. The drying process can include a low temperature stage and a high temperature stage followed by a cooling period. To ensure a clean environment during the drying process, it is currently performed using an evacuated chamber. Because of the vacuum, there is little or no heat conduction. Rather, the heat transfer occurs by contact between the particles and the inside surface of the chamber. However, the process can take a long time due to the lack of thermal convection and the need to heat or cool the chamber between different drying stages, sometimes 12-24 hours for a typical batch. Also, to ensure homogeneous drying of the material, the material can be mechanically mixed or agitated in the chamber during the process. However, such mixing/agitation can pose a risk of metallic contamination in the material, which could cause defects in the lithium ion battery.